Can I apply coordinate transformation in a structures table

[Anonymous]

In Ireland we have two coordinate systems, the old system ING (Irish National Grid) and the newer one ITM (Irish Transverse Mercator). Most practices now work to ITM but our Water utility body insist on coordinates to the old coordinate system. This causes us a lot of wasted time converting from one system to the other.

Is it possible to work to one coordinate system but have the "pipe network structures table" output the coordinate of the 2nd coordinate system?

[rl_jackson · Accepted solution]

I consistently use a "local system" based on an assumed position, and then have the transform set my drawing in State Plane Grid system from the Drawing Settings at the Transform Tab.

However, I was looking at the structure options and it doesn't appear that it will provide the coordinate value of the local system and the grid system, that I could see. This is not to say there couldn't be some sort of hack that you might use a point table to accomplish your goal, which would allow for a local and "grid" system in your instance.

Edit: Another thought that comes to mind is using an expression that would convert the current system to the old system with the structure table or label.

[jameshitt]

@rl_jackson Can expressions be used in Civil 3D labels?

If there isn't an option to make it work in Civil 3D labels, it sounds like it might be a messy data sets export/import type deal...possibly also using expressions... Yeesh. This sounds like a good suggestion for future features.

[rl_jackson]

Sure expressions can be used in C3D labels, I do it with Curb elevations where I have the Elevation for the Flowline (FL) and to get the elevation of the Top of Curb (TC) i create an expression called TC which is Elevation+0.5.  I really see no difference in the OP's expression as long as he doesn't have a rotation in the equation, if its a straight forward North and East shift, it should be simple.

[Anonymous]

@rl_jackson I was thinking along the expression option too but I don't see expressions in the Structure Table Styles settings. I only see them in the Structure Label styles settings.

[rl_jackson]

Your correct, I was thinking out loud before looking, that is the only drawback. No expressions in Tables.

[Anonymous · Accepted solution]

@rl_jackson It works. I added the expression to Structure Labels and it is available in the properties pull down in the Table Style. Thanks so much for pointing me in the right direction.

[Pointdump]

@Anonymous ,
Your expression just does an X shift? Have you checked the results for accuracy? The Irish National Grid and Irish Transverse Mercator have not only different False Eastings, but also different False Northings and Grid Scale Factors:

PROJCS["TM65 / Irish National Grid (deprecated)",
     PARAMETER["scale_factor",1.000035],
     PARAMETER["false_easting",200000],
     PARAMETER["false_northing",250000],

PROJCS["IRENET95 / Irish Transverse Mercator",
     PARAMETER["scale_factor",0.99982],
     PARAMETER["false_easting",600000],
     PARAMETER["false_northing",750000],

Dave

[Anonymous]

I am doing an x shift based on converting a local point in the centre of my site. I know this is not ideal. Is it possible to make the actual conversion in an expression?

[marianne.mcdonaldTZVTF]

Hi Dave,
Does this expression work as a general transform from ING to ITM? When I use the Civil3D transform operation, it draws with an offset so the objects aren't in the correct place

[Pointdump]

Hi Marianne,
I wouldn't attempt an expression. If you have Civil 3D objects, like alignments, surfaces, etc, use the >>>Transfomation Tool<<<. If you just have dumb AutoCAD linework, use >>>Attach/Query<<<.
Dave

[marianne.mcdonaldTZVTF]

Attach/Query is what I've been using, but for some reason it's not quite moving to the correct place - not sure if it's a rounding error or something in my settings. Thanks anyway

[Pointdump]

Marianne,
Can you post some sample data and your workflow/steps?
Dave

[marianne.mcdonaldTZVTF]

Hi Dave,

Example files attached.
Example map tile is in the correct location in ING and the wrong location in ITM
Workflow as follows:

• Attach PDF (PDF has coordinates in ING at each corner, that's why I'm not importing directly to ITM)
• Scale & correctly locate in ING drawing
• ADEQUERY command in ITM drawing
• Objects transform almost correctly but not quite

[Pointdump]

Marianne,
Thanks for posting your drawings.
I opened a new drawing and assigned IRENET95.IrishTM Coordinate System.
Attach'ed/Query'ed both drawings. All linework matches, but does not match Bing Live Maps.
I also Attach'ed/Query'ed each drawing into the other. I saw no differences.
Dave

[marianne.mcdonaldTZVTF]

Thanks for looking - that's the result I got. If I find a reason why or a fix, i'll post it here

[Pointdump]

Marianne,
So your original data is a PDF?
How did you geo-reference the linework? County Cork has parcel data in shapefile format, but I don't think it's free.
Dave